This invention relates to planar photoluminescent lamps, and more particularly, to a planar photoluminescent lamp having two electrodes and which emits light by fluorescent phenomena.
Thin, planar, and relatively large area light sources are needed in many applications. Backlights must often be provided for liquid crystal displays (LCD) to make them readable in all environments. Because present active matrix LCDs allow only up to approximately 5% light transmission, the backlights must produce enough light to permit readability in low light conditions. Thin backlights for LCDs are desired to preserve as much as possible the LCDs"" traditional strengths of thin profile, low cost, and readability in high ambient lighting conditions while permitting readability at numerous angles.
Many demanding challenges exist for engineering a thin planar source of uniform light. If incandescent lamps or LEDs are used as the light source, then optics for dispersing and diffusing light from the multiple point sources to the planar viewing surface must be provided to avoid local bright or dim spots. Despite recent advances, LEDs are spectrally limited, which reduces their applicability for situations where white light is desired. Additionally, provision must be made to dissipate the heat generated by the incandescent or LEDs or alternatively, to utilize only high-temperature materials for LCDs. Electroluminescent lamps suffer from having a relatively low brightness but are sometimes selected as solutions that require only low light display outputs.
Another choice for generating light for a display is photoluminescent technology, including fluorescent lamps. Fluorescent lamps have the advantage of being relatively efficient and capable of generating sufficiently bright light. Tubular fluorescent lamps of about 2 mm in diameter are often used as a backlight, but have the undesirable property of uneven light distribution. Planar fluorescent lamps are well known in the art, having been described, for example, in U.S. Pat. Nos. 3,508,103; 3,646,383; and 3,047,763. Typically, such lamps in the prior art are formed by molding a housing and a cover, each from a piece of glass and sealing the glass pieces to form a sealed enclosure. A selected gas and a fluorescent material are placed in the sealed enclosure for emitting light when an electrical field is applied. Typical fluorescent lamps often have bare metal electrodes, which are exposed to ionized particles of the gas thereby causing undesirable sputtering effects.
Where the enclosure is formed entirely from glass, fabrication can be difficult and the resulting lamp is often quite fragile. A stronger lamp can be made by using thicker pieces of glass to form a lamp having thicker walls. However, increased glass thickness results in a undesirably thicker and heavier lamp, is more difficult to fabricate and may attenuate some light output.
Planar fluorescent lamps having sidewalls formed from metal with a serpentine channel defined by internal walls are known from U.S. Pat. Nos. 2,508,103 and 2,405,518. The sidewalls and internal walls of the serpentine channel provides support for the top and bottom covers. However, longer serpentine channels require undesirably higher electrode voltages that are necessary to ionize the selected gases. Large display areas using planar fluorescent lamps having such internal walls require that many planar fluorescent lamps be tiled together to provide large areas of illumination.
A need remains therefor, for a thin, lightweight, planar lamp having a substantially uniform display that is easily manufacturable, is readily scaleable to larger display sizes, is temperature tolerant, and is relatively durable.
The limitations of prior lamps are overcome by the present invention, which is an open chamber photoluminescent lamp and a method of producing an open chamber photoluminescent lamp. In a sample embodiment, a gas-filled photoluminescent planar lamp contains a photoluminescent material that emits visible light in response to ultraviolet energy emitted from an ionized gas. The lamp contains first and second opposing glass plates that are made from glass material having a loss tangent of less than around 0.05%. A plurality of sidewalls are coupled to the peripheral edges of the first and second plates so that a chamber is formed that contains the gas and photoluminescent material. The lamp also contains first and second electrodes disposed along an exterior surface of at least one of the first and second plates so that an electrical field is created when electrical power is applied to the electrodes so that the electric field interacts with the gas contained within the chamber.
In another embodiment, the lamp may further contain a plurality of spacers that are distributed between the first and second glass plates at predetermined locations so that the first and second plates will be maintained at a predetermined distance from each other. The spacers may be further manufactured from glass material that is transmissive to ultraviolet radiation. The lamp may further contain a plurality of spacers positioned between the first and second plates so that the first and second plates will be maintained at a distance of less than around 0.5 mm from each other.
In yet another embodiment, the lamp contains sidewalls that are sized to maintain the first and second plates at a distance of less than around 0.5 mm between the first and second plates.
In yet another embodiment the first plate is less than around 1 mm thick. The lamp may be further constituted such that the distance from the exterior surface of the first plate to the exterior surface of the second plate is less than around 5.0 mm.
In yet another embodiment, the electrodes are disposed along the exterior surface of only one of the first and second plates. Alternatively, the first electrode may be disposed along the exterior surface of the first plate and the second electrode may be disposed along the exterior surface of the second plate.
In further embodiments, the lamp comprises a first plate having a dielectric constant of greater than around 5, the lamp comprises at least one plate being manufactured from planar glass material that is substantially free of sodium, and the lamp further comprises a layer of photoluminescent material applied to an inner surface of at least one of the first and second plates to luminesce in response to ionization of the contained gas.
In another example embodiment, a gas-filled photoluminescent planar lamp contains a photoluminescent material that emits visible light when the gas emits ultraviolet energy in response to a plasma discharge. The lamp contains first and second opposing glass plates that are made from glass material having a dielectric constant greater than 5.0. A plurality of sidewalls are coupled to the peripheral edges of the first and second plates so that a chamber is formed that contains the gas and photoluminescent material. The lamp also contains first and second electrodes disposed along an exterior surface of at least one of the first and second plates so that an electrical field is created when electrical power is applied to the electrodes so that the electric field interacts with the gas contained within the chamber.